In a storage apparatus which manages various types of drives (storage devices), when the input/output of data to and from the drives is controlled by using a SAS (Serial Attached SCSI) protocol as the backend interface, a SAS controller is used as the controller. With this type of controller, when an IO (Input Output)-based command is received from a CPU (Central Processing Unit) which processes commands received from a host computer, the controller assigns a tag number to each IO and accesses the drive according to the IO to which the tag number was assigned. Each drive performs IO processing based on the tag number, and sends the processing result to the controller. Here, when a chip reset is instructed from the CPU to the controller, the controller executes Power On Reset, and is initialized. Subsequently, when the status of failure is recovered and an IO-based command is sent from the CPU to the controller, the controller assigns a tag number to each IO and accesses the drive according to the IO to which the tag number was assigned. Here, in the controller, a tag number that is the same as the tag number assigned before the chip reset is assigned to each IO, and, in cases where the chip reset is executed before the previous IO processing is completed and the IO having the same tag number is assigned to the same drive, information to the effect that a tag overlap has occurred is notified from each drive to the controller, and IO processing cannot be executed in the respective drives. As this type of system, proposed is a type configured to facilitate the communication between one initiator and SATA (Serial AT Attachment) devices (refer to PTL 1).